The best option is to have a way to use service accounts (bot accounts) with restricted access to your google sheets.

Using unity's default API Key requires you to make the google spreadsheet public, and using the OAuth, well you already know the friction it creates to mainatin the developer's google account as testers every seven days.

That's why I created my own plugin to seamlessly integrate authentication using google service account without loosing all the features the current Google Sheet Extension offer.

Here's the github repo and the youtube tutorial I made. Try it out and let me know.

Youtube Link: - https://www.youtube.com/watch?v=bsEYavsGfJs

Github Repo - https://github.com/IamBiswajitSahoo/UnityLocalizationGoogleSheetsSA